Firstly, it is important to understand that all classification of an email as “spam” or “not spam” is done on the receiving end, not the sending end. This is because, if it was done the other way round, all spammers would, of course, classify their mails as “not spam” – i.e. all such classification would be worthless.
This means that ultimately, only the administrators of the recipients email account can know why the email was wrongly classified, and what to do about that. Perhaps their spam-filters are badly configured. Perhaps something in your email looked quite like a pattern used by spammers. But generally, only they can say. As such, the best thing to do is to ask them to find out. In the case of some systems (e.g. GMail), when you look at a message in the “spam” folder, it tells you why the mail was identified as spam at the top. So, the recipient, having found the mail in their “spam” folder, can read the reason why there.
Generally, it can help to not place too many website links in emails you send. For example, if you already have one or more in the footer, perhaps removing these might help. Also, if you are in the habit of sending out mass-mailings from your email account (i.e. the same mail to lots of people), this may result in your domain getting a reduced “reputation score” on other people’s systems – this can mean that other mails are looked at as more suspicious than they would be otherwise, even if these mass-mailings are not themselves spam. (Please note that sending of all spam, i.e. unsolicited commercial email, via a Simba Hosting service, is prohibited).
Unfortunately, spam filters are often unreliable. Spammers are always testing and tweaking their campaigns to try to make sure they get past spam filters. If spam filters could be 100% accurate, then spam would not exist. Experience shows that even huge mail providers, like GMail, regularly mis-classify large amounts of mail – especially if the recipient (i.e. GMail user) does not carefully press the “Spam” or “Not Spam” button on every mis-classified mail and continue to do so. If they don’t, then the system becomes self-re-inforcing: in future it assumes its previous decisions were correct, and becomes more confident in making similar decisions.
Posted in: Questions concerning e-mail